North Carolina General Statutes Chapter 66. Commerce and Business § 66-27.1. Certain automatic hot water tanks or heaters to have approved relief valves; installation or sale of unapproved relief valves forbidden

(a) No individual, firm, corporation or business shall install, sell or offer for sale any automatic hot water tank or heater of 120-gallon capacity or less, except for a tankless water heater, which does not have installed thereon by the manufacturer of the tank or heater an American Society of Mechanical Engineers and National Board of Boiler and Pressure Vessel Inspectors approved type pressure-temperature relief valve set at or below the safe working pressure of the tank as indicated, and so labeled by the manufacturer's identification stamped or cast upon the tank or heater or upon a plate secured to it.

(b) No individual, firm, corporation or business shall install, sell, or offer for sale any relief valve, whether it be pressure type, temperature type or pressure-temperature type, which does not carry the stamp of approval of the American Society of Mechanical Engineers and the National Board of Boiler and Pressure Vessel Inspectors.